The present invention relates generally to a cable termination assembly, and is particularly concerned with a field installable underwater cable termination assembly for electrical, optical, or hybrid electro-optical cables.
Field installable termination assemblies are used in underwater or other high pressure environments in order to connect a cable exposed to a high pressure environment to an underwater device at a lower pressure. In the present state of the art field installable termination assemblies (FITA), conductors of the cable to be terminated fan out from the cable and are passed through one or more seals, eventually entering an oil chamber which is pressure balanced to the ambient environment. Thus, the individual jacketed wires are in the oil. As the conductors fan out from the inner core of the cable, they pass through seals at the point where they separate from each other. Break-out boot seals are typically used at the separation point for this purpose. These break-out boot seals are often in the oil chamber. In many known FITAs, both the conductors and the sealed junctions where they separate from one another are located in the oil-filled compensation chamber. The conductors then go on within the oil chamber to terminate to other conductors or to the attachment points of connectors. Again, boot seals seal these junctions. The result is that there are typically numerous seals and jacketed conductors within the oil chamber.
There are a number of problems associated with the current FITA terminations. The conductor jackets and the seals within the oil chamber are barriers which are intended to keep the high pressure oil from rushing into the cable interstices, including those between the individual stranded wires of individual conductors. If any one of these seals, or the conductor jacket, should fail, oil will be forced into the cable. The compensation chamber will then either collapse or it will spring a leak, allowing sea water to enter. The result is a catastrophic failure. Another failure mode may arise when the conductors pass from the chamber in which they exit the cable, also known as the break-out volume, into the oil-filled volume, where the conductors are unable to adequately support the hydrostatic pressure imposed in deep water. In such cases, the conductors may collapse axially and fail. U.S. Pat. Nos. 4,907,980, 4,907,982 and 4,940,416 of Wagaman et al. all describe cable termination assemblies in which the conductors extend through a cavity filled with a dielectric fluid. In U.S. Pat. No. 6,364,677 of Nysveen et al., each conductor is terminated in a separate, liquid-filled and pressure compensated interior chamber.
Another less common failure mode occurs when gel-filled cables are employed. In this mode, as cables are passed over handling devices such as pulleys, the gel is xe2x80x9cmilkedxe2x80x9d or pumped towards the terminations. This can unseat boot seals and result in subsequent failure. Still another failure mode, not well understood, occurs when cable is retrieved quickly from great ocean depths. In this case, pressurized gas may expand within the cable, and seals can be unseated. Failure can also occur when the cable is under axial compression, as can happen during handling. In this case, the cable pistons inward, passing into the compensation chamber and destroying the internal structure.
It is an object of the present invention to provide a new and improved cable termination assembly which is field installable and suitable for use in underwater cable systems. The termination assembly may connect the cable to another cable, a connector, an oil-filled hose cable assembly, or an equipment housing.
According to one aspect of the present invention, a cable termination assembly is provided which comprises an outer casing having a first end for sealably receiving the end of a cable carrying a plurality of conductors and a second end, the casing having an internal chamber, a high pressure barrier plug in the casing sealing the chamber, and a plurality of feedthrough devices extending through the barrier, the conductors in the cable extending from the cable end through the first chamber up to the barrier plug. The chamber is filled with a solid material which is initially pourable to substantially fill the chamber after the cable conductor ends are connected to the feedthrough devices on the first side of the barrier plug, and is then allowed to cure to provide a solid filler for the chamber, gripping or holding the conductors firmly in place. The material may be any suitable pourable material which cures to form a solid, such as a solid epoxy or elastomer. The material may be a dielectric, but this is not essential.
This termination assembly may be used for electrical cables, optical cables, or hybrid cables. When the termination assembly is designed to terminate electrical or hybrid cables, the individual jacketed conductors from the cable are not terminated in an oil chamber. Instead, they are terminated in a chamber containing a solid filler material. This completely eliminates all failure modes resulting from having the electrical conductors or jacketed wires of the terminated cable within the oil filled compensation chamber. The solid material which substantially fills the internal chamber will hold each conductor or wire to resist any tendency for the wire to collapse axially. A second chamber, which is oil-filled and pressure balanced, may be provided on the opposite side of the high pressure barrier or plug, with electrical conductors or wires connecting each feedthrough device through the second chamber to an oil filled hose assembly or the like within an equipment housing at a lower pressure than the surrounding environment. With this arrangement, an impenetrable barrier is provided between the cable which is exposed to the high pressure environment and the oil filled, pressure balanced chamber, substantially or completely avoiding the potential failure modes when oil is forced into the cable or due to axial collapse of a conductor.
In the case of a hybrid cable carrying both optical fibers and electrical conductors, the arrangement will be similar except that an optical fiber end seal assembly will be provided in the barrier for feedthrough of the optical fibers, for example the end seal assembly as described in U.S. Pat. No. 6,321,021 of Cairns et al., the contents of which are incorporated herein by reference. In the case of an optical cable, the barrier plug will have one or more optical fiber end seal assemblies only.
The cable which is terminated may be either armored or unarmored. Two such cable termination assemblies may be secured back-to-back to form a cable-to-cable splice. In this case, the oil filled compensation chamber could be eliminated, and solid filler material may fill the chamber on each side of the barrier or penetrator. Alternatively, the cable may be terminated to one half of an underwater connector of any type, with the barrier being replaced by the connector end wall and the conductors in the cable connected to terminals in the connector half.
The assembly of this invention provides a fully sealed, high pressure, field-installable cable termination assembly configured to allow termination of cables independent of their construction at high ambient pressures. Where one or more cables are to be terminated, the or each cable will be terminated to a respective module forming a high pressure barrier, and the or each module in turn will connect to the oil filled compensation chamber through an end wall of the compensation assembly, which may be mounted in a panel or bulkhead of an equipment housing. The respective modules provide full mechanical and pressure barriers for the cable to compensation chamber interface. Since individual electrical conductors do not enter the compensation chamber, the most common failure modes are eliminated. The solid material filling the module chamber diminishes cable pistoning due to changing pressure or handling of the cable.